[PM/ThinLTO] Port the ThinLTO pipeline (both components) to the new PM.

Based on the original patch by Davide, but I've adjusted the API exposed
to just be different entry points rather than exposing more state
parameters. I've factored all the common logic out so that we don't have
any duplicate pipelines, we just stitch them together in different ways.
I think this makes the build easier to reason about and understand.

This adds a direct method for getting the module simplification pipeline
as well as a method to get the optimization pipeline. While not my
express goal, this seems nice and gives a good place comment about the
restrictions that are imposed on them.

I did make some minor changes to the way the pipelines are structured
here, but hopefully not ones that are significant or controversial:

1) I sunk the PGO indirect call promotion to only be run when we have
   PGO enabled (or as part of the special ThinLTO pipeline).

2) I made the extra GlobalOpt run in ThinLTO just happen all the time
   and at a slightly more powerful place (before we remove available
   externaly functions). This seems like general goodness and not a big
   compile time sink, so it didn't make sense to *only* use it in
   ThinLTO. Fewer differences in the pipeline makes everything simpler
   IMO.

3) I hoisted the ThinLTO stop point pre-link above the the RPO function
   attr inference. The RPO inference won't infer anything terribly
   meaningful pre-link (recursiveness?) so it didn't make a lot of
   sense. But if the placement of RPO inference starts to matter, we
   should move it to the canonicalization phase anyways which seems like
   a better place for it (and there is a FIXME to this effect!). But
   that seemed a bridge too far for this patch.

If we ever need to parameterize these pipelines more heavily, we can
always sink the logic to helper functions with parameters to keep those
parameters out of the public API. But the changes above seemed minor
that we could possible get away without the parameters entirely.

I added support for parsing 'thinlto' and 'thinlto-pre-link' names in
pass pipelines to make it easy to test these routines and play with them
in larger pipelines. I also added a really basic manifest of passes test
that will show exactly how the pipelines behave and work as well as
making updates to them clear.

Lastly, this factoring does introduce a nesting layer of module pass
managers in the default pipeline. I don't think this is a big deal and
the flexibility of decoupling the pipelines seems easily worth it.

Differential Revision: https://reviews.llvm.org/D33540

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@304407 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 123 insertions, 18 deletions

diff --git a/lib/Passes/PassBuilder.cpp b/lib/Passes/PassBuilder.cpp
index abc53e97aa72..eb81e58b9b0e 100644
--- a/lib/Passes/PassBuilder.cpp
+++ b/lib/Passes/PassBuilder.cpp
@@ -164,7 +164,8 @@ static cl::opt<bool> EnableGVNHoist(
     "enable-npm-gvn-hoist", cl::init(false), cl::Hidden,
     cl::desc("Enable the GVN hoisting pass for the new PM (default = off)"));
 
-static Regex DefaultAliasRegex("^(default|lto-pre-link|lto)<(O[0123sz])>$");
+static Regex DefaultAliasRegex(
+    "^(default|thinlto-pre-link|thinlto|lto-pre-link|lto)<(O[0123sz])>$");
 
 static bool isOptimizingForSize(PassBuilder::OptimizationLevel Level) {
   switch (Level) {
@@ -345,6 +346,9 @@ PassBuilder::buildFunctionSimplificationPipeline(OptimizationLevel Level,
   LPM2.addPass(IndVarSimplifyPass());
   LPM2.addPass(LoopIdiomRecognizePass());
   LPM2.addPass(LoopDeletionPass());
+  // FIXME: The old pass manager has a hack to disable loop unrolling during
+  // ThinLTO when using sample PGO. Need to either fix it or port some
+  // workaround.
   LPM2.addPass(LoopUnrollPass::createFull(Level));
 
   // We provide the opt remark emitter pass for LICM to use. We only need to do
@@ -454,14 +458,10 @@ static void addPGOInstrPasses(ModulePassManager &MPM, bool DebugLogging,
 }
 
 ModulePassManager
-PassBuilder::buildPerModuleDefaultPipeline(OptimizationLevel Level,
-                                           bool DebugLogging) {
-  assert(Level != O0 && "Must request optimizations for the default pipeline!");
+PassBuilder::buildModuleSimplificationPipeline(OptimizationLevel Level,
+                                               bool DebugLogging) {
   ModulePassManager MPM(DebugLogging);
 
-  // Force any function attributes we want the rest of the pipeline te observe.
-  MPM.addPass(ForceFunctionAttrsPass());
-
   // Do basic inference of function attributes from known properties of system
   // libraries and other oracles.
   MPM.addPass(InferFunctionAttrsPass());
@@ -504,16 +504,16 @@ PassBuilder::buildPerModuleDefaultPipeline(OptimizationLevel Level,
   GlobalCleanupPM.addPass(SimplifyCFGPass());
   MPM.addPass(createModuleToFunctionPassAdaptor(std::move(GlobalCleanupPM)));
 
-  // Add all the requested passes for PGO Instrumentation, if requested.
+  // Add all the requested passes for PGO, if requested.
   if (PGOOpt) {
     assert(PGOOpt->RunProfileGen || PGOOpt->SamplePGO ||
            !PGOOpt->ProfileUseFile.empty());
     addPGOInstrPasses(MPM, DebugLogging, Level, PGOOpt->RunProfileGen,
                       PGOOpt->ProfileGenFile, PGOOpt->ProfileUseFile);
-  }
 
-  // Indirect call promotion that promotes intra-module targes only.
-  MPM.addPass(PGOIndirectCallPromotion(false, PGOOpt && PGOOpt->SamplePGO));
+    // Indirect call promotion that promotes intra-module targes only.
+    MPM.addPass(PGOIndirectCallPromotion(false, PGOOpt && PGOOpt->SamplePGO));
+  }
 
   // Require the GlobalsAA analysis for the module so we can query it within
   // the CGSCC pipeline.
@@ -562,17 +562,30 @@ PassBuilder::buildPerModuleDefaultPipeline(OptimizationLevel Level,
       createModuleToPostOrderCGSCCPassAdaptor(createDevirtSCCRepeatedPass(
           std::move(MainCGPipeline), MaxDevirtIterations, DebugLogging)));
 
-  // This ends the canonicalization and simplification phase of the pipeline.
-  // At this point, we expect to have canonical and simple IR which we begin
-  // *optimizing* for efficient execution going forward.
+  return MPM;
+}
+
+ModulePassManager
+PassBuilder::buildModuleOptimizationPipeline(OptimizationLevel Level,
+                                             bool DebugLogging) {
+  ModulePassManager MPM(DebugLogging);
+
+  // Optimize globals now that the module is fully simplified.
+  MPM.addPass(GlobalOptPass());
 
   // Run partial inlining pass to partially inline functions that have
   // large bodies.
   if (RunPartialInlining)
     MPM.addPass(PartialInlinerPass());
 
-  // Eliminate externally available functions now that inlining is over -- we
-  // won't emit these anyways.
+  // Remove avail extern fns and globals definitions since we aren't compiling
+  // an object file for later LTO. For LTO we want to preserve these so they
+  // are eligible for inlining at link-time. Note if they are unreferenced they
+  // will be removed by GlobalDCE later, so this only impacts referenced
+  // available externally globals. Eventually they will be suppressed during
+  // codegen, but eliminating here enables more opportunity for GlobalDCE as it
+  // may make globals referenced by available external functions dead and saves
+  // running remaining passes on the eliminated functions.
   MPM.addPass(EliminateAvailableExternallyPass());
 
   // Do RPO function attribute inference across the module to forward-propagate
@@ -671,6 +684,87 @@ PassBuilder::buildPerModuleDefaultPipeline(OptimizationLevel Level,
 }
 
 ModulePassManager
+PassBuilder::buildPerModuleDefaultPipeline(OptimizationLevel Level,
+                                           bool DebugLogging) {
+  assert(Level != O0 && "Must request optimizations for the default pipeline!");
+
+  ModulePassManager MPM(DebugLogging);
+
+  // Force any function attributes we want the rest of the pipeline to observe.
+  MPM.addPass(ForceFunctionAttrsPass());
+
+  // Add the core simplification pipeline.
+  MPM.addPass(buildModuleSimplificationPipeline(Level, DebugLogging));
+
+  // Now add the optimization pipeline.
+  MPM.addPass(buildModuleOptimizationPipeline(Level, DebugLogging));
+
+  return MPM;
+}
+
+ModulePassManager
+PassBuilder::buildThinLTOPreLinkDefaultPipeline(OptimizationLevel Level,
+                                                bool DebugLogging) {
+  assert(Level != O0 && "Must request optimizations for the default pipeline!");
+
+  ModulePassManager MPM(DebugLogging);
+
+  // Force any function attributes we want the rest of the pipeline to observe.
+  MPM.addPass(ForceFunctionAttrsPass());
+
+  // If we are planning to perform ThinLTO later, we don't bloat the code with
+  // unrolling/vectorization/... now. Just simplify the module as much as we
+  // can.
+  MPM.addPass(buildModuleSimplificationPipeline(Level, DebugLogging));
+
+  // Run partial inlining pass to partially inline functions that have
+  // large bodies.
+  // FIXME: It isn't clear whether this is really the right place to run this
+  // in ThinLTO. Because there is another canonicalization and simplification
+  // phase that will run after the thin link, running this here ends up with
+  // less information than will be available later and it may grow functions in
+  // ways that aren't beneficial.
+  if (RunPartialInlining)
+    MPM.addPass(PartialInlinerPass());
+
+  // Reduce the size of the IR as much as possible.
+  MPM.addPass(GlobalOptPass());
+
+  // Rename anon globals to be able to export them in the summary.
+  MPM.addPass(NameAnonGlobalPass());
+
+  return MPM;
+}
+
+ModulePassManager
+PassBuilder::buildThinLTODefaultPipeline(OptimizationLevel Level,
+                                         bool DebugLogging) {
+  // FIXME: The summary index is not hooked in the new pass manager yet.
+  // When it's going to be hooked, enable WholeProgramDevirt and LowerTypeTest
+  // here.
+
+  ModulePassManager MPM(DebugLogging);
+
+  // Force any function attributes we want the rest of the pipeline to observe.
+  MPM.addPass(ForceFunctionAttrsPass());
+
+  // During the ThinLTO backend phase we perform early indirect call promotion
+  // here, before globalopt. Otherwise imported available_externally functions
+  // look unreferenced and are removed.
+  MPM.addPass(PGOIndirectCallPromotion(true /* InLTO */,
+                                       PGOOpt && PGOOpt->SamplePGO &&
+                                           !PGOOpt->ProfileUseFile.empty()));
+
+  // Add the core simplification pipeline.
+  MPM.addPass(buildModuleSimplificationPipeline(Level, DebugLogging));
+
+  // Now add the optimization pipeline.
+  MPM.addPass(buildModuleOptimizationPipeline(Level, DebugLogging));
+
+  return MPM;
+}
+
+ModulePassManager
 PassBuilder::buildLTOPreLinkDefaultPipeline(OptimizationLevel Level,
                                             bool DebugLogging) {
   assert(Level != O0 && "Must request optimizations for the default pipeline!");
@@ -893,9 +987,16 @@ static Optional<int> parseDevirtPassName(StringRef Name) {
   return Count;
 }
 
+/// Tests whether a pass name starts with a valid prefix for a default pipeline
+/// alias.
+static bool startsWithDefaultPipelineAliasPrefix(StringRef Name) {
+  return Name.startswith("default") || Name.startswith("thinlto") ||
+         Name.startswith("lto");
+}
+
 static bool isModulePassName(StringRef Name) {
   // Manually handle aliases for pre-configured pipeline fragments.
-  if (Name.startswith("default") || Name.startswith("lto"))
+  if (startsWithDefaultPipelineAliasPrefix(Name))
     return DefaultAliasRegex.match(Name);
 
   // Explicitly handle pass manager names.
@@ -1090,7 +1191,7 @@ bool PassBuilder::parseModulePass(ModulePassManager &MPM,
   }
 
   // Manually handle aliases for pre-configured pipeline fragments.
-  if (Name.startswith("default") || Name.startswith("lto")) {
+  if (startsWithDefaultPipelineAliasPrefix(Name)) {
     SmallVector<StringRef, 3> Matches;
     if (!DefaultAliasRegex.match(Name, &Matches))
       return false;
@@ -1109,6 +1210,10 @@ bool PassBuilder::parseModulePass(ModulePassManager &MPM,
 
     if (Matches[1] == "default") {
       MPM.addPass(buildPerModuleDefaultPipeline(L, DebugLogging));
+    } else if (Matches[1] == "thinlto-pre-link") {
+      MPM.addPass(buildThinLTOPreLinkDefaultPipeline(L, DebugLogging));
+    } else if (Matches[1] == "thinlto") {
+      MPM.addPass(buildThinLTODefaultPipeline(L, DebugLogging));
     } else if (Matches[1] == "lto-pre-link") {
       MPM.addPass(buildLTOPreLinkDefaultPipeline(L, DebugLogging));
     } else {